1. Field of the Invention
The present invention relates to a recording and reproducing apparatus and a recording and reproducing method. More particularly, the present invention is concerned with a technology for raising an accessing speed, at which data recorded in a disk is accessed, using a cache memory.
2. Description of the Related Art
In the past, a cache memory has been incorporated in a disk drive in efforts to speed up input/output (I/O) processing to be performed by the disk drive. The cache memory is used as a temporary preservation place for reading and writing. The cache memory having a small storage capacity of about several tens of megabytes or less is generally adopted. For reading or writing of data from or in a disk, if the data is not accessed in the cache memory (there is no hit), an access time gets longer due to addition of a seek time.
As a technique for raising a hit ratio of a cache memory, look-ahead caching is known. Look-ahead caching is such that when intended data is read from a disk, plural data items arrayed successively to the data are all read and stored in a cache memory. Namely, before a request for reading the succeeding array of data items is issued, the data items are read in advance from the disk and stored in the cache memory. Therefore, when the reading request is actually issued, the data items can be read quickly from the cache memory.
For reading successive data items from a disk, the technique has proved very useful because data items read beforehand and stored in the cache memory can be used to meet a reading request. However, the technique is not very useful in a case where data items are read randomly. In this case, the hit ratio of the cache memory is not high.
As a technique for solving the above problem, a technology in which when a specific sector in a floppy disk is accessed, the contents of an entire track including the specific sector are stored in a hard disk using the hard disk as a cache is described in, for example, JP-A-2000-172448 (Patent Document 1). Accordingly, a cache hit ratio to be attained when the specific sector whose contents are stored in the cache is accessed is raised.